What is Melanonychia?
Melanonychia is a brown or black discoloration (pigmentation) of your nail that occurs when melanin (the pigment that gives color to your skin) gets deposited in the nail plate. 1, 2
Understanding the Basics
Think of melanonychia as a "pigmented streak" or band running through your nail. It appears as:
- A brown to black line or band running from the base of your nail (where it grows from) to the tip
- Sometimes the entire nail may be darkened
- Most commonly appears as a longitudinal (lengthwise) stripe 2, 3
What Causes It?
Melanonychia can happen for many different reasons, ranging from completely harmless to serious:
Common Benign (Non-Dangerous) Causes:
- Normal variation - especially common in people with darker skin tones
- Trauma or injury to the nail
- Medications - certain chemotherapy drugs and other medications 4
- Fungal infections of the nail 5, 6
- Pregnancy or hormonal changes
- Benign moles in the nail matrix (the area where your nail grows from)
Serious Cause to Rule Out:
Why It Matters
The most important reason to evaluate melanonychia is to rule out melanoma (skin cancer), which can initially present as a dark streak in the nail. 2, 8 However, melanonychia is most often benign - the challenge is distinguishing between harmless pigmentation and something that needs treatment.
When to Worry - Red Flags
You should see a doctor urgently if you notice: 7
- A new pigmented line in a nail, especially if it's changing
- The dark band is wider than 3mm or involves more than 40% of the nail width 9
- Irregular borders or multiple colors within the band
- Hutchinson's sign - pigmentation spreading onto the skin around the nail (the cuticle or nail fold)
- The nail is breaking down or becoming damaged (dystrophy)
- Bleeding or pain in the affected nail
- Only one nail affected (especially in adults) 10, 9
- Change in appearance over time - getting wider, darker, or more irregular
What Happens Next?
If your doctor is concerned about your melanonychia, they may:
- Examine it with dermoscopy - a special magnifying tool to look at the pigment pattern more closely 8
- Take your medical history - asking about trauma, medications, family history
- Perform a biopsy - taking a small sample of the nail matrix tissue to examine under a microscope if melanoma is suspected 8, 11
The key message: Most melanonychia is harmless, but any new or changing pigmented band in your nail should be evaluated by a healthcare provider to ensure it's not melanoma. Early detection of nail melanoma is critical for good outcomes, but unfortunately, there's often a delay of about 2 years in diagnosis because it can look like other benign conditions 2.